Method and apparatus for detecting particles in a flow

Abstract

An apparatus for detecting particles in a flow comprises a probe 1 positioned so that it projects into the flow and is charged triboelectrically by the particles in the flow. An electric circuit is coupled to the probe 1 and includes evaluating means for monitoring a signal from the probe 1 and for providing an output in dependence on the signal generated by the triboelectric charging of the probe 1. The part of the probe 1 that projects into the particle flow comprises an electrically conducting core covered with an insulating layer 2 which insulates the core from the particle flow.

What is claimed is:  
     
       1. A method of detecting particles flowing along a emitted through the stack in which a probe is positioned so that it projects into the flow of particles and is charged by the particles in the flow characterized in that the part of the probe that projects into the particle flow comprises an electrically conducting core covered with an insulating layer which insulates the core from the particle flow and the A.C. component of a signal from the probe is evaluated to provide an indication of the particle flow. 
     
     
       2. Method as claimed in claim  1  in which the particles are suspended in a fluid flow and the probe is charged triboelectrically by the particles in the fluid flow. 
     
     
       3. A method as claimed in claim  1  in which the fluid is a gas and the particles are liquid or solid particles suspended in the gas. 
     
     
       4. A method as claimed in claim  1  in which the A.C. component of the signal from the probe is filtered to exclude high frequency components of the signal. 
     
     
       5. A method as claimed in claim  4  in which the A.C. component of the signal from the probe is filtered to limit the frequency to below about 5 Hz. 
     
     
       6. A method as claimed in claim  1  or claim  4  in which the A.C. component of the signal is filtered to exclude low frequency components of the signal. 
     
     
       7. A method as claimed in claim  6  in which the A.C. component of the signal is filtered to limit the frequency to above about 0.1 Hz. 
     
     
       8. Apparatus for detecting particles flowing along a stack and emitted through the stack comprising a probe to be positioned so that it projects into the flow to be charged by the particles in the flow, and an electric circuit coupled to the probe characterized in that the part of the probe to project into the particle flow comprises an electrically conducting core covered with an insulating layer which insulates the core from the particle flow, and the electric circuit has evaluating means for monitoring an A.C. component of the signal from the probe for providing an output in dependence on the signal generated by the triboelectric charging of the probe. 
     
     
       9. Apparatus as claimed in claim  8  characterized in that the probe is in the form of a rod. 
     
     
       10. Apparatus as claimed in claim  9  characterized in that the rod is of circular cross-section. 
     
     
       11. Apparatus as claimed in claim  8  in which the electric circuit comprises filter means for filtering out high frequency components of the signal. 
     
     
       12. Apparatus as claimed in claim  11  in which the filter means are for limiting the frequency of the A.C. component of the signal to below about 5 Hz. 
     
     
       13. Apparatus as claimed in claim  8  or claim  11  in which the electric circuit comprises filter means for filtering out low frequency components of the signal. 
     
     
       14. Apparatus as claimed in claim  13  in which the filter means are for limiting the frequency of the A.C. component to above about 0.1 Hz. 
     
     
       15. A method of detecting particles flowing along a stack and emitted through the stack in which a probe is positioned so that it projects into the flow of particles and is charged by the particles in the flow characterized in that the part of the probe that projects into the particle flow comprises an electrically conducting core covered with an insulating layer which insulates the core from the particle flow, the signal from the probe is filtered to block the D.C. signal and the A.C. signal is evaluated to provide an indication of the particle flow. 
     
     
       16. Apparatus for detecting particles flowing along a stack and emitted through the stack comprising a probe to be positioned so that it projects into the flow to be charged by the particles in the flow, and an electric circuit coupled to the probe characterized in that the part of the probe to project into the particle flow comprises an electrically conducting core covered with an insulating layer which insulates the core from the particle flow, and the electric circuit has filter means for blocking the D.C. signal from the probe an evaluating means for monitoring the filtered A.C. signal for providing an output in dependence on the signal generated by the triboelectric charging of the probe. 
     
     
       17. A method of detecting particles flowing along a stack and emitted through the stack in which a probe is positioned so that it projects into the flow of particles and is charged by the particles in the flow characterized in that the part of the probe that projects into the particle flow comprises an electrically conducting core covered with an insulating layer which insulates the core from the particle flow, that the signal from the probe is filtered to limit the signal to an A.C. signal of frequency above about 0.1 H z  and the A.C. signal is evaluated to provide an indication of the particle flow. 
     
     
       18. Apparatus for detecting particles flowing along a stack and emitted through the stack comprising a probe to be positioned so that it projects into the flow to be charged by the particles in the flow, and an electric circuit coupled to the probe characterized in that the part of the probe to project into the particle flow comprises an electrically conducting core covered with an insulating layer which insulates the core from the particle flow, and the electric circuit has filter means for limiting the signal from the probe to an A.C. signal of frequency above about 0.1 H z  and evaluating means for monitoring the filtered A.C. signal for providing an output in dependence on the signal generated by the triboelectric charging of the probe. 
     
     
       19. A method of detecting particles flowing along a stack and emitted through the stack in which a probe is positioned so that it projects into the flow of particles and is charged by the particles in the flow characterised in that the part of the probe that projects into the particle flow comprises an electrically conducting core covered with an insulating layer which insulates the core from the particle flow and a signal from the probe is filtered to exclude frequency components below about 0.1 Hz and above about 5 Hz and is evaluated to provide an indication of the particle flow. 
     
     
       20. A method of detecting particles flowing along a stack and emitted through the stack in which a probe is positioned so that it projects into the flow of particles and is charged by the particles in the flow characterised in that the part of the probe that projects into the particle flow comprises an electrically conducting core covered with an insulating layer which insulates the core from the particle flow, the insulating layer being substantially thinner than the conducting core, and a signal from the probe is evaluated to provide an indication of particle flow. 
     
     
       21. A method as claimed in claim  20 , in which the signal for the probe is filtered to exclude frequency components below about 0.1 Hz. 
     
     
       22. A method as claimed in claim  20 , in which the signal for the probe is a current signal which is converted into a voltage signal, said voltage signal being passed through signal processing means which block the DC component of the voltage signal to generate a processed voltage signal and said processed voltage signal being subsequently evaluated to provide an indication of the particle flow. 
     
     
       23. A method of detecting particles flowing along a stack and emitted through the stack in which a probe is positioned so that it projects into the flow of particles and is charged by the particles in the flow characterised in that the part of the probe that projects into the particle flow comprises an electrically conducting core covered with an insulating layer which insulates the core from the particle flow and the probe generates a current signal which is converted into a voltage signal, said voltage signal being passed through signal processing means which block the DC component of the voltage signal to generate a processed voltage signal, and, said processed voltage signal being subsequently evaluated to provide an indication of the particle flow. 
     
     
       24. A method as claimed in claim  23 , in which said processed voltage signal excludes frequency components below about 0.1 Hz. 
     
     
       25. Apparatus for detecting particles suspended in a gas flow flowing along a gas flow path emitted through a sack, the apparatus comprising: 
       a probe projecting into the gas flow path for detecting particles in the gas flow along the stack,  
       a wall defining a boundary of the gas flow path,  
       the probe comprising an electrically conducting core and a covering layer,  
       the covering layer being electrically insulating and serving to block conduction of a DC current from the surface of the probe through the insulating layer to the electrically conducting core of the probe,  
       the probe being fixed in the wall with the electrically conducting core electrically insulated from the wall, and  
       an electric circuit connected to the electrically conducting core of the probe for evaluating the signal from the core of the probe for providing an output in dependence on the signal generated by the charging of the probe.  
     
     
       26. Apparatus as claimed in claim  25 , in which the probe is in the form of a rod. 
     
     
       27. Apparatus as claimed in claim  26 , in which the rod is of circular cross-section. 
     
     
       28. Apparatus as claimed in claim  25 , in which the electric circuit comprises filter means for filtering out high frequency components of the signal. 
     
     
       29. Apparatus as claimed in claim  28 , in which the filter means are for limiting the frequency the AC component of the signal to below about 5 Hz. 
     
     
       30. Apparatus as claimed in claim  25 , in which the electric circuit comprises filter means for iltering out low frequency components of the signal. 
     
     
       31. Apparatus as claimed in claim  30 , in which the filter means are for limiting the frequency of the AC component to about 0.1 Hz. 
     
     
       32. A method for detecting particles flowing in a gas flow along a stack and emitted through the stack in which a probe including a portion which comprises an electrically conducting core covered by an insulating layer which insulates the core from particle flow is positioned so that said portion projects into the flow of particles in the stack and is charged triboelectrically by particles in the flow and the quantities of electrical charges transferred to the probe are evaluated to provide an indication of the particle flow in the gas flow, wherein, in order to reduce the effect of variations in gas flow related variables other than those relating to particle flow, an alternating component in the signal caused by the triboelectrical charging of the probe is monitored, the alternating component of the signal from the probe is filtered to exclude high frequency components of the signal and the magnitude of the residual alternating component is itself used to give an indication of the particle flow through the stack. 
     
     
       33. The method according to claim  32  in which the alternating component of the signal from the probe is filtered to limit the frequency to about 0.10 Hz. 
     
     
       34. The method according to claim  32  in which said insulating layer is substantially thinner than said conducting core.